The invention relates to a method of removing dents from parts made of sheet metal, in particular lacquered parts of an automobile body, as well as an apparatus for implementing this method.
The removal of dents from pieces of sheet metal with the aim of restoring, as far as possible, an original (flat or curved) shape is a task that occurs in many branches of industry and the trades. Although a large number of technical procedures and devices have been developed to accomplish this task, some of which are commercially available, the problem is still often solved by the manual efforts of trained personnel. This entails considerable expense.
Probably the most economically important application of dent-removing methods and apparatus is the repair of motor vehicles.
Hail damage to cars, in particular to new cars parked in the storage yards of automobile manufacturers, alone accounts for an annual average of several hundred million DM in Germany. The dents caused by hailstones are usually small and rounded, so that their shape and dimensions often allow them to be pressed out manually. However, somewhat larger indentations that cause a plastic deformation of the metal cannot be removed in this way. To eliminate such relatively large dents various kinds of apparatus have been proposed. These operate, for example, on the basis of locally reduced pressure or on a magnetic principle, and are intended to restore the original shape of the affected piece of metal without elaborate dismantling procedures. Application of such apparatus in some cases demands great experience and hence must be carried out by correspondingly highly paid workers, and nevertheless often is not as successful as would be wished. In many cases, therefore, additional laborious lacquering work is inevitable.
The objective of the invention is thus to disclose a method and an apparatus for the removal of dents from pieces of sheet metal that are distinguished in particular by low production and operating costs and high service value.
This objective is achieved with respect to its methodological aspect by a method with the characteristics given in claim 1 and with respect to the apparatus by an arrangement with the characteristics given in claim 11.
The invention includes the essential idea that to remove relatively small dents thermal energy is introduced into a piece of sheet metal in a narrowly circumscribed region thereofxe2x80x94specifically, the region of the dentxe2x80x94and the metal is caused to spring back into the original state by the resulting mechanical tension gradient. Surprisingly, the inventors discovered that this action can be achieved even with warming to comparatively low temperatures, well below critical temperatures at which the customary surface coatings of sheet-metal parts (in particular, the lacquer coating of an automobile body) undergo thermal damage. This enables a very broad application of the proposed method, especially for eliminating small sites of damage to automobiles such as the hailstone damage described above.
In a preferred embodiment of the method, the local warming is produced by targeted application of radiation, a substantial proportion of which is in the near-infrared region, in particular, in the wavelength region between 800 nm and 2 xcexcm. In this embodiment the method can be implemented with an apparatus that is particularly simple and economical to manufacture and can be operated by workers with no special experience. By suitably adjusting the irradiation wavelength to the characteristics of the materials involved (the metal and whatever coating is present), it becomes possible in particular to introduce the energy substantially directly into the metal, while largely avoiding the coating.
Alternatively, the dented metal part can be locally warmed by an inductive means or by a directed stream of hot air.
A crucial consideration is that the warming is done in a targeted and limited manner, and in particular is substantially punctate in the central region and/or annular in the peripheral region of the dent that is to be removed. As a result, the tension gradient that causes the metal to spring back into the original shape is built up in a controlled manner. In the case of coated metal parts, the local warming is in particular limited to a final temperature, which is low enough that irreversible changes in the coating (e.g., a layer of lacquer) cannot yet occur. Even under this limiting condition, suitable preliminary setting of the size and shape of the warming zone and, where appropriate, of the rate of heating preserve sufficient degrees of freedom to enable indentations of various sizes and shapes to be eliminated from metal pieces made of various materials, in particular lacquered sheet steel.
Especially for repairing the latter, according to tests carried out by the inventors it has proved sufficient to warm the region of the dent in a lacquered automobile body locally to a temperature in the range between 100xc2x0 C. and 200xc2x0 C.
In an advantageous further development of the idea underlying the invention, during the local warming the momentary shape of the metal part is monitored, and when springing back into the original shape is detected, the response is to terminate the warming process. This further development makes it possible partially to automate the method. In combination with the above-mentioned temperature limitation, this embodiment in particular enables the method to be carried out even by personnel with no special training and experience.
When the metal parts to be processed are of exactly the same kind and have similar coatingsxe2x80x94as is the case, for instance, when hail damage to motor vehicles is being repairedxe2x80x94the above-mentioned temperature limitation can be achieved by a suitable design of the heating device, so that where appropriate it is possible to eliminate the need for temperature measurement. It is somewhat more complicated for the method to include the measurement and regulation of momentary temperature, but an apparatus capable of these functions can also be used for a wide variety of sheet metals and coatings.
Implementation of the method can be additionally facilitated with a design in which the site of the local warming is marked by a visible light beam, and the heating device is directed towards the spot of light thus produced on the metal part.
An apparatus for carrying out the method described above comprises in particular a heating device that functions in a substantially non-contact manner, which advantageously comprises an adjustable heat-introduction region. Such a device can be optimally adapted to indentations of various sizes and to metal sheets that differ in thickness.
In an especially simple and economical embodiment the heating device operates in the near-infrared region (NIR) and exhibits a predetermined directional characteristic for the emitted radiation. Such a heating device preferably comprises an approximately punctate halogen light source, which is operated at a surface temperature of 2500 K or more, in particular 2900 K or more.
In an embodiment that is preferred because of its versatility regarding possible applications, the heating by NIR radiation has a variable directional characteristic, achieved in particular by an adjustable aperture or apertures and/or mechanical adjustment meansxe2x80x94in particular to modify the position or shape of a reflector.
In accordance with the preferred further developments of the basic idea of the method, as described above, the apparatus in particular comprises a temperature-measurement device to monitor the surface temperature of the metal part in the warming region, which is advantageously connected to a control input of the heating device so that a temperature regulation (at least a temperature limitation) is produced in dependence on the result of the temperature measurement. In an advantageous embodiment the temperature-measurement device incorporates a non-contact sensor, specifically a radiation pyrometer.
In another preferred embodiment of the proposed apparatus an aiming means is provided with which to direct the heating device towards the region of a dent. This aiming means specifically comprises a radiator for visible light that is fixedly attached to the heating device and is either self-focussing or provided with associated focussing means, so as to produce a narrowly circumscribed spot of marking light on the metal part.
This marker enables the operator to position the heating device precisely with respect to the dent.
An additional preferable feature is the provision of an optical measuring device to monitor the momentary shape of the metal part, which can be constructed for instance as a laser-triangulation device. As a result of the measurement of the surface shape of the sheet metal, in particular this device sends out a xe2x80x9cfinishedxe2x80x9d signal as soon as it detects that the indented area has sprung back so as to restore the original state of the metal part. This signal can be used to turn off the heating device directly and/or can be displayed visually to the operator.
It is especially advantageous to use a single light source for both the aiming and the measuring device in combination, and in this regard it is particularly advantageous to employ a laser radiation source, for example an economical laser-diode device.